This invention relates to distributed processing systems and, more particularly, to broadcast systems for use in a distributed switching network.
Multi-line telephone key stations, sometimes referred to as "trader turrets", are widely used in rapid communication networks such as trading operations in banks, brokerage houses, and other financial institutions. Telephones of this type provide direct access to a large number of telephone lines with a line being selected by the depression of a single key on the key station. Trader turrets generally include at least thirty line keys and often have several hundred. Trader turrets are normally used in networks where the number of lines is greater than the number of telephones whereas, with normal telephone key stations, the number of telephones exceeds the number of lines.
Each telephone key station may have access to other telephone key stations in the system within a trading room and to a large number of outside lines and private lines. Each telephone user may be connected to several lines or terminals at the same time in a conferencing mode.
A large trading room can include many transactions each involving many millions of dollars. A typical trading transaction involves a rapid series of short telephone conversations to, for example, locate traders having the desired security for sale at the best price. A typical call lasts only for a few second and there may be many calls per minute during the course of a single transaction.
An important feature required in such trader network systems is a provision at each telephone key station for displaying the current status of each of the lines accessible to the station. The line status display usually takes the form of a continually lit indication for a "busy" line, a flashing indication for a line on "hold" or "ringing", and no indication for a free line. A prior system for monitoring line status is disclosed in U.S. Pat. No. 4,998,275 issued to Braunstein et. al. In addition, a trader turret telephone station must be capable of indicating the line which is in use so that the trader can at all times identify the other party on the line.
In prior switching networks used in key telephone systems, line status indication was generally a dedicated activity involving the continuous polling of line cards by a processor and the continuous distribution of line status data. Line status information, unlike voice or data transmission, is continuously transmitted across the system on a polled rather than an event basis. Additionally, the implementation of the polling type line status transmission system is such that the only information available via the system are simple not-in-use, ringing, busy, and hold line indications.
In large key systems continuous transmission of the status of every line in the system results in high traffic loading on the polling mechanism or excessive delay in status signalling. Due to the high traffic loading and the system-specific implementation of the line status transmission system, the system is also not adaptable to other system functions such as the broadcast of system data and event occurences.